Roller rocker arms 1

[sierra4000]

Hi guys!
Can you tell me something about roller rockers? Is there any benefits between original rocker arms and roller rocker arms if stay on same arm ratio? I wondering how much influence does to the friction losses? Is there any benefits if i use lighter roller rocker?

Thank you for ideas

Radek

 

[sierra4000]

First of all, I am interested in the real performance gains for the 7000 to -8000 rpm.

Again than you

 

[bigTomHanks]

Yes roller rockers are better due to reduced friction and better operating geometry between the pushrod/valve. This is marginal in most engine applications that operate in the standard 1000-5000 rpm range. In the range that you are proposing there are more gains to be had and may be worth the investment. I would argue however that an OHC setup would better for an engine you planned to run that fast for various reasons, mainly because the real issues of high revving a pushrod engine start to become more of a factor.

 

[sierra4000]

Thanks,
I must direct my question to debunk. I talking about low stroke OHV engine.

 

[MikeHalloran]

You might bet a performance gain if you increase the rocker ratio, just by getting more valve lift. ... which you may get away with because of reduced side force on the valve guides. But you should do a precision or CAD layout of the entire valve train before going ahead, to check clearances and angles and such.

What you should get, with rocker arms of the same ratio, is better valve guide life. If that's not a problem now, e.g. because you throw away the heads for other reasons with few miles on them, roller rockers may be a waste of money.



Mike Halloran
Pembroke Pines, FL, USA

 

[tbuelna]

sierra4000-

Can you be more specific in what you mean by an OHV "roller rocker"? Do you mean a rolling element (needle) bearing at the fulcrum? A roller at the contact with the valve tip? Or both?

A needle bearing at the fulcrum does not really provide much benefit over a well designed plain bearing in terms of friction. A needle bearing does not work well with the high-frequency oscillatory motion occurring at the rocker fulcrum. There tends to be a fair amount of roller skidding (and friction) when the rocker rotation stops and reverses direction. The plain bearing has the advantage of lower mass/inertia, and also results in a stiffer installation.

A roller at the tip adds a bit of mass, but it also reduces friction and reduces side loading on the valve stem.

Regards,
Terry

 

[sierra4000]

Thank you all,
Yes you're right! I talking about "roller at the tip". For clarification here is some pictures, original vs. custom. What is the influence of weight and the material and arm stiffness ?Thanks for your opinion!

https://fbcdn-sphotos-h-a.akamaihd...._=1397782004_51810e78e3f98786b8e0f5357b9b4e8b

https://fbcdn-sphotos-h-a.akamaihd...._=1397791650_33122957e94ff86aefd60ce247afcfb3

 

[MikeHalloran]

In general, weight is bad, stiffness is good.
... but at high rpm in a pushrod engine, everything is a spring, so the dynamics can get complicated enough that rules of thumb will not predict what's going to happen.

Let's back up a bit.
Are you trying to solve a specific problem that's been bothering your engine, or
are you just trying to go faster?




Mike Halloran
Pembroke Pines, FL, USA

 

[sierra4000]

OK, Just trying increase high rpm range and achieve maximum rpm with the help of reduction mass and friction. I increased bore from 77mm to 79,5mm, use forged pistons with lower compress height from 40mm to 30mm but stay on original 70mm stroke. So i must use longer conrods. I chose lighter forged H-beam conrods. I achieve lower pistons side trust with help of smaller conrod angularity from 16° to 15° (angle of conrods vs cylinder). As i say i stay on original stroke but i polished original crankshaft to reduce drag. So as you can see i try to do maximum of possible. Next step are rocker mods. And now I wondering if it is worth investing to roller rocker. Can a higher stiffness, lower weight and lower friction losses of roller rockers improve performance? Or it is like placebo effect? All the time i talking about old air cooled paralel 2 cylinder Fiat engine with original 652ccm (after mods 695ccm)

Thanks
Radek

 

[MikeHalloran]

Can a higher stiffness, lower weight and lower friction losses of roller rockers improve performance?

Not enough to measure with ordinary tools.

... i try to do maximum of possible

There's your answer.

I wouldn't bother unless the stock rockers are a problem.
How many have you broken so far?



Mike Halloran
Pembroke Pines, FL, USA

 

[sierra4000]

Ok Mike, I understand ... better to invest the money elsewhere...
Thank you very much!

Radek

 

[pontiacjack]

It appears that someone offers an aftermarket rocker/shaft setup for your engine- or is that for some other engine? If it's for yours, then enough people are breaking Fiat rocker arms to warrant creating that product.

As for saying (guessing?) whether you'll need them- I'd want to know how much increase in valve spring force you'll need to spin it to 8,000 RPM.

 

[BrianPetersen]

The engine that you are working with only has 2 main bearings (both cylinders are between the bearings) and there is a big counterweight in the middle, and no balance-shaft, either. If you are trying to get that to rev, you have much greater issues than worrying about rocker arms!

The "built" versions of those engines that I'm aware of (and certainly there could be others) only spin to 7000 rpm and that's limited by the bottom end staying together. If you operate it near the critical speed of the crankshaft assembly, it's going to go boom.